There are many applications in which it is necessary to provide substantially continuous power from an internal combustion engine. For example, in natural gas well field operations, an internal combustion engine may be provided to operate compressors and other equipment. Such internal combustion engines may operate unattended twenty-four hours a day, seven days a week. In such applications, it is necessary to maintain a charge in the battery associated with such internal combustion engines, which typically is a wet cell battery.
Such engines may use an alternator, which is driven by the engine. An example of such an alternator is the alternator 10 shown in FIG. 1. That alternator 10 has an output 12 connected to a wet cell battery or batteries 14. The alternator 10 may include an internal regulator 16 that monitors the output voltage of the alternator through an internal feedback loop 18, which typically is located inside the alternator. The internal regulator may maintain the voltage output by the alternator 10 at typically a constant voltage, for example, 14 volts in a 12 volt system. A disadvantage of such an alternator 10 is that the battery 14 may be subjected to environmental conditions during the course of a day or a season that may require an increase or decrease in charging voltage output by the alternator. For example, on a relatively cold day, it may be desirable to increase the charging voltage from the output 12 from 14 volts to 14.2 volts or 14.3 volts. Additionally, there may be line losses between the output 12 of the alternator 10 and the battery 14 so that the voltage actually delivered at the battery terminals may be less than that measured at the output of the alternator by the internal regulator 16.
As shown in FIG. 2, to address this situation, an alternator 20 may include an internal regulator 16 that is connected by a wire 22 to the terminals 24 on the battery 14 to provide a remote sense capability. Typically, the wire 22 runs alongside the larger current-carrying conductor 26 from the output 12 to the battery 14. An alternator 20 equipped with an external wire 22 connected to battery terminals 24 provides a more accurate charging voltage because it cancels out any voltage drop along the conductor 26 or due to resistance at connection points at the output 12 or at the battery 14. Although a system comprised of an alternator 20 and external wire 22 for remote sense capability has the advantage of low cost of manufacture and a feedback loop superior to that of the alternator 10 of FIG. 1, there is a disadvantage in that they introduce an additional failure mechanism into the electrical system.
If the wire 22 providing feedback to the internal regulator 16 is compromised, or its connections to the battery or alternator are compromised, the alternator 20 loses its feedback loop, and the internal regulator is no longer able to control the voltage of the output 12. In such a condition, the output voltage of the alternator 20 would then rise to unsafe levels. This event has the potential to destroy the alternator 20, the battery 14 and possibly other sensitive electronics. Because of the potential harm resulting from this failure mode, the benefits provided by such a remote sense alternator system may not justify the risks.
Other systems such as temperature compensation circuits or custom external regulators also share this same problem. If the feedback loop is compromised the alternator can no longer control its output voltage, which may have the potential of destroying components of the electrical system. Accordingly, there is a need for an alternator system and method that utilizes a remote sensor, but eliminates the risks associated with a breakdown in the feedback circuit.